Sum of Numbers on Invisible Faces
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The faces of a polyhedron are labeled 1, 2, 3, …. Find the sum of the numbers on the invisible faces.
Contributed by: Izidor Hafner (October 2013)
Open content licensed under CC BY-NC-SA
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"Sum of Numbers on Invisible Faces"
http://demonstrations.wolfram.com/SumOfNumbersOnInvisibleFaces/
Wolfram Demonstrations Project
Published: October 23 2013